I see two accessibility problems with the links current Google search results page.

1. They are using the hover attribute to display underlines, but they did NOT do the same for :focus. If you are on a keyboard, links are particularly invisible.
2. The majority of the links are actually gray and plaintext. They include the links at the top (i.e. "Web, Images, News...) and the links connecting to Google Circles.
I have to ask - why have links to a Google Circle is they are practically invisible?

In terms of removing the underline for in-text links, I am not a fan, but am OK with it when link text is bold face (this can provide some contrast for those with color vision issues).

I also think using a shade of blue different from black is important because most people with color vision issues can perceive blue. But the blue shouldn't be so dark that it merges with the rest of the text. Unfortunately, I see a lot of that these days.

Elizabeth

P.S. I will note that the top hits for "link usability" indicate that underlining is good practice.